Relay is a necessary element in the general application of electronic devices. But, frequently either the voltage withstanding capability of relay is insufficient, or the current flowing through the relay is relatively large, which generates an arc, and results in a situation being selected from a group consisting of the life-span of the relay is shortened in the minor case, the contacts of the relay are melted down in the major case, and even a fire could be broken out to cause an industrial safety problem in the worst case. In a different situation, the voltage across the contacts of the relay is raised such that the tolerated current flowing through the relay is dramatically decreased and results in being one of the states that the space of the product is occupied but the expected requirements are not achieved in the minor case and a relatively more complex circuit is in need since the relay is not applicable in the major case. Thus, the development of a relay system including a relay protection circuit having a relatively better effectiveness in suppressing the arc is a necessity.
In general, the protection circuits suppressing an arc for a relay in the prior art are added over the trip point of the relay, e.g., the protection circuit having a resistor, the protection circuit having an RC circuit (including a resistor and a capacitor) and the protection circuit having a diode etc., which could not achieve an effective trip of the trip point under one of a relatively large voltage and a relatively large current, and there are other problems such as the relay could not be effectively and fully employed as specified by the specification.
Base on the above mentioned considerations, a relay protection circuit including only two simple components, a high-impedance element and an energy storage element, which make the relay operate within the relatively maximum range of the specification and the problems caused by the arc could also be solved to avoid the increase of the costs and the industrial accidents.
Generally speaking, relatively the most annoying problem is how to eliminate the arc, and the most difficult one of which is to eliminate the arc generated by a DC power supply when a relay is used in a power system (such as an isolated switch at the output terminal of a power supply). Especially when the voltage across the two terminals of a contact is larger than the rated voltage of relay, frequently either the voltage across the two terminals of the contact is lowered, or the elements, which could stand for relatively higher voltages, are in need so as to prevent one of the industrial accidents and the electricity breakdown of the power supply at the customer side. The general approach for eliminating the arc generated by the DC power supply includes the employments of the various protection circuits in the prior art, which are described as follows.
As shown in FIG. 1, it is a circuit diagram of a conventional relay system 1 including a relay protection circuit 11 having an RC circuit. The protection circuit having a RC circuit 11 includes a resistor R1 and a capacitor C1 electrically connected to the resistor R1 in series, and the RC circuit 11 is electrically connected to the trip point of the relay X1 in parallel. In which, the resistance of R1 needs to be carefully notice to avoid consequences that the arcs are not totally eliminated when the relay is turned on and off continuously, which results in the melting down of the contacts, and the relay protection circuit 11 will totally lose its functions when the voltage across the two terminals of certain contact of the relay X1 is larger than the specification of the relay X1.
In FIG. 2, it is a circuit diagram of a conventional relay system 2 including a relay protection circuit 21. The relay protection circuit 21 includes a capacitor C1 electrically connected to the trip point of the relay X1 in parallel. The capacitor C1 is charged to its saturation voltage V1 rather quickly if there is a relatively larger arc existed and results in the consequences that the arc is not totally eliminated and the contacts of the relay X1 are melted down.
Please refer to FIG. 3, which is a circuit diagram of a conventional relay system 3 including a relay protection circuit 31. The relay protection circuit 31 includes two relays (X1 and X2) being electrically connected to each other in series to eliminate the arc. Referring to FIG. 4, it shows a circuit diagram of a conventional relay system 4 including a relay protection circuit 41. The relay protection circuit 41 includes a double pole single throw relay X1. Each of the relay protection circuits 31 and 41 can be used to eliminate the arcs generated by the relay systems 3 and 4 respectively. However, the relay protection circuit 31 including two relays (X1 and X2) could result in the problems such as the volume of the product is relatively larger and the manufacturing costs are relatively higher though the arc generated by the relay system 3 could be eliminated. The drawback of using the relay protection circuit 41 as shown in FIG. 4 to eliminate the arc generated by the relay system 4 is that it can not be employed in a circuit having a relatively larger current due to the limitations of the double pole single throw relays thereof.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the applicant finally conceived the relay protection circuit and the controlling method thereof having the relatively better effectiveness for suppressing the DC arc.